The present invention relates to a deformable mirror primarily intended for use as a beam train optic, and relates more particularly to a unique configuration of a deformable mirror capable of operating in an environment of an extremely high incident energy burst, such as at the National Ignition Facility now under design.
It is most important that a support for a high energy burst mirror be capable of withstanding the complete environment in which it operates without degradation. Except for the structure disclosed in copending U.S. patent application Ser. No. 08/982,920 entitled HIGH-ENERGY-BURST DEFORMABLE MIRROR, none of the current designs of such supports are capable of doing this. The invention disclosed in the aforementioned application does provide a lower cost solution to meet high energy requirements, but the mirror faceplate is a flat surface on both sides, and all the buttons are joined simultaneously under heat and pressure. The present invention is designed to work in the National Ignition Facility now being designed to produce sources of energy for the world by controlled fission. This facility requires 200 deformable mirrors for operation. The prior art consists of conventionally designed deformable mirrors where the actuators are attached directly to the back of the mirror with epoxy as seen in FIG. 1. These mirror-to-actuator connections have failed in controlled tests. In addition, Lawrence Livermore National Labs now has produced a configuration with a circumferential joint to the back of the deformable mirror as seen in FIG. 2. This configuration will deteriorate with time since the joint still experiences part of the incident energy.
Empiric data indicates that conventionally designed deformable mirrors fail in high burst energy mode environments because the epoxy joint between the back of the mirror and the top of the actuator gets too hot for even high temperature epoxies to survive (typically 400 to 600 degrees F.). In addition, analysis indicates that because of the short time duration of the energy burst, any metal subjected to the energy will get hot at the incident surface, but within one millimeter of depth, the temperature will rise no more than several degrees F. The next energy burst is done typically seven hours later, a more than adequate time for the system to thermally stabilize itself to initial conditions.
DEFORMABLE mirrors used in facilities such as the NIF are thus subjected to very high energy beams for very short duration. Typically 10 Joules/cm.sup.2 for 200 microseconds. Conventionally designed deformable mirrors as seen in FIG. 1 would be destroyed by the heat generated because of absorption at the joint 3 between the back of the faceplate 1 and the attached actuator 2. Likewise, the other design connection between the faceplate 1' and the actuator 2' with the circumferential joint connection 3' undesirably absorbs energy at the joint interface.
Accordingly, an object of the invention is to produce a deformable mirror that has a low technical risk to fabricate and meets all of the requirements for use in a high energy burst mode without any degradation of performance of physical attributes.
It is another object of the present invention to provide a continually supported deformable mirror support that meets all of the requirements for use in a high energy burst mode without any degradation of performance of physical attributes.
A further object of the invention is to provide a joint to be used in a continually supported deformable mirror connected to a positioning actuator which operates without any degradation of its structural integrity as is now experienced with conventionally designed deformable mirrors.
Yet a further object of the invention is to provide a joint at the back of the deformable mirror faceplate that is connectable to a replaceable actuator and is capable of sustaining high temperature environments and using the drop in temperature of metal in series with this joint to attach such actuators with conventional epoxy.
Still a further object of the invention is to provide a support system of the aforementioned type which reduces the fabrication risk by integrally machining the buttons into the back surface of the faceplate.
Still a further object of the invention is to produce a joint where an epoxy joint is used and wherein the epoxy joint does not realize direct radiation from an energy source.
Yet still a further object of the invention is to provide a joint where a mechanical glass-to-metal joint is provided which does not induce high stress concentrations loads on the glass.